Aerial refueling is a process of transferring fuel from a tanker aircraft to a receiver aircraft during flight. Aerial refueling allows the receiver aircraft to extend its range or remain airborne longer. By aerial refueling after take-off, the receiver aircraft can allow a take-off with a greater payload, since a maximum take-off weight can be met by carrying less fuel. Probe and drogue, and flying boom are two main refueling systems. Aerial refueling is a well-established means in aviation to extend the range and duration/loiter of airborne aircraft. With the advent of unmanned aerial vehicles (UAV) and the absence of human pilots, autonomous aerial refueling poses new challenges.